hard nut to crack vs tight spot

hard nut to crack

noun
  • Used other than figuratively or idiomatically: see hard, nut, crack. 

  • A problem that is challenging to solve. 

  • A situation, person, group, etc. which is difficult to overcome or deal with. 

  • A place, opportunity, etc. to which it is difficult to gain entry. 

  • An amount that is difficult to finance. 

tight spot

noun
  • Used other than figuratively or idiomatically: see tight, spot. 

  • A difficult position. 

How often have the words hard nut to crack and tight spot occurred in a corpus of books? (source: Google Ngram Viewer )